Holmes devoted her energies to teaching academic, or college preparatory, curriculum at the high school level for more than thirty years, mostly in Chicago, Illinois.

There Holmes distinguished herself further by leading the history department at Du Sable High School for several years, an unusual leadership role for any woman in those times.

Margaret Holmes demonstrated in her work as an educator and civic activist how African-American sororities supported women "to create spheres of influence, authority and power within institutions that traditionally have allowed African Americans and women little formal authority and real power.

Flagg's ambition and abilities were demonstrated by her going to Howard at a time when only 1/3 of 1% of African Americans and 5% of whites of eligible age attended any college.

[2][5] With Ethel Hedgeman and Lavinia Norman, Margaret helped to plan the sorority by refining their first constitution, drafted by Lucy Diggs Slowe.

For nine years, Flagg served as a history, Latin and English teacher at the same Baltimore high school as fellow founder Lucy Diggs Slowe.

[2] By studying during summers, Flagg earned a Master of Arts degree in philosophy in 1917 from Columbia University in New York.

Both the chapter and national organization raised funds in the 1920s and 1930s for scholarships, and contributed to the NAACP and Urban League.

In Paris, France, Margaret met the famous African American dancer Josephine Baker.